1. Field of the Invention
The present invention is in the field of cardiology, and more specifically is a method for obtaining a continuous sequence of horizontal vectorcardiograms from an ambulatory patient over an extended interval of time by use of a five-electrode lead system.
2. Description of the Prior Art
Since its introduction in 1949, the concept of dynamic portable monitoring of cardiac performance has grown widely. Modern technology in the form of Holter recording systems was introduced in 1961 and now provides more than 24-hours of continuous electrocardiographic data. The Holter technique was disclosed by Holter in a paper entitled "New Method for Heart Studies" in Science, Vol 134, pp 1214-1220 (1961). More recently, ambulatory monitoring and recording techniques have been adapted to recording ambulatory blood pressure and continuous electroencephalograms. From this relatively rapidly changing technology in Holter recording has emerged the innovation disclosed herein of deriving a horizontal plane vectorcardiogram from a two-channel Holter recording of electrocardiographic data. Such derived adjunctive data enhances the clinical utility of routine ambulatory electrocardiography.
Since the inception of dynamic ambulatory electrocardiography procedures, Holter recording examination has been performed utilizing a two-channel lead system employing a modified chest V.sub.1 lead and a chest bipolar lead V.sub.5. This lead system was specifically chosen to facilitate diagnosis and identification of cardiac dysrhythmias, particularly anomalous extrasystoles, as seen in lead V.sub.1, and to best detect left ventricular myocardial ischemia by employing a commonly used sensitive exercise lead, chest bipolar V.sub.5. Early investigations of anomalous extrasystoles sought to interpret the simultaneous analog electrocardiographic signals derived from this V.sub.1 and V.sub.5 lead system, and led to a search for some way to integrate or combine these two channels of electrocardiographic data. The present invention grew out of this long-felt need.
Vectorcardiogram studies using magnetic tape recordings to display the inscription of the vector in slow motion have been previously reported in a paper "Time Exapnsion in Vectorcardiography: the advantages of Magnetic Tape Recording" by Estes, et al. in American Heart Journal Vol. 63, pp. 98-100 (1962). These studies used the Frank lead system or a modified McFee lead system, and were designed to measure horizontal (X), longitudinal (Y), and saggital (Z) plane forces. Much of the merit of the present procedure resides in the simplification achieved by deriving the horizontal plane vectorcardiogram from commonly used electrocardiographic V.sub.1 and V.sub.5 data. This adjunctive vectorcardiographic data complements the analog electrocardiographic V.sub.1 and V.sub.5 signal data by providing a visual integrated picture of those simultaneous signals.
Previous studies have already indicated merit in the vectorcardiographic analysis of anomalous and ectopic beats for identifying the site of origin of ectopic beats. These descriptions, however, have not gained wide clinical interest. This lack of interest may in part be due to the relatively large number of electrodes necessitated by standard vectorcardiographic methods, and the possible difficulty in some instances of recording chance ectopic beats on standard vectorcardiographic methods. Accordingly, clinicians generally seem less inclined to seek and utilize X, Y and Z axis analog data in the routine management of patients.